The present invention relates generally to a process and system for biodiesel production and more specifically to the conversion of any high free fatty acid feedstocks to fatty acid methyl esters through both esterification and transesterification reactions. The process and system economically produce biodiesel when compared to current technologies.
The background art is characterized by U.S. Pat. Nos. 1,659,790; 2,290,609; 2,383,596; 2,383,599; 2,383,601; 2,494,366; 2,808,421; 2,875,221; 3,102,129; 3,459,736; 4,164,506; 4,267,393; 4,303,590; 4,364,743; 4,371,470; 4,668,439; 4,695,411; 4,698,186; 4,839,287; 4,956,286; 5,399,731; 5,424,467; 5,434,279; 5,514,820; 5,525,126; 5,697,986; 5,713,965; 5,908,946; 6,013,817; 6,015,440; 6,090,959; 6,127,561; 6,174,501; 6,211,390; 6,262,285; 6,288,251; 6,398,707; 6,399,800; 6,440,057; 6,489,496; 6,500,974 and 6,642,399 B2; and by U.S. Patent Application Nos. 2003/00229238 and 2003/0083514 the disclosures of which patents and patent applications are incorporated by reference as if fully set forth herein.
Fatty acid methyl esters (FAMEs) produced from fats and oils are being investigated in numerous settings as replacements for petroleum-derived materials, particularly diesel fuel. There is continued and growing interest in the use of renewable resources as replacements for petroleum-derived chemicals. It has long been known that diesel engines can use the triglycerides from fats and oils as fuels. However, their use eventually results in engine failure. The problems have been examined and certain solutions have been proposed in the methods described in U.S. Pat. Nos. 6,174,501 and 6,015,440. This problem is alleviated by conversion of the fatty acids found in lipids into their simple esters, usually methyl or ethyl esters. Such a process is described in U.S. Pat. No. 6,398,707. An increasing body of evidence indicates that these esters perform well in essentially unmodified diesel engines and that they can reduce the output of particulate and hydrocarbon pollutants relative to petroleum-diesel fuel. The term “biodiesel” is applied to these esters, which are also being explored as replacements for nonrenewable chemicals in other applications, including cleaning agents, fuel additives, and substitutes for other organic solvents. Those applications have been investigated in processes described in U.S. Pat. No. 5,713,965. The invention disclosed herein can be applied to the production of FAMEs for these applications as well.
It can be appreciated that processes for biodiesel production have been in use for years. Typically, a process for biodiesel synthesis is comprised of the conversion of fatty acids with acid catalysis such as a process described in U.S. Pat. No. 4,164,506, the conversion of triglycerides with base catalysis such as the processes described in U.S. Pat. Nos. 2,383,601 and 2,494,366, or conversion of both free fatty acids and triglycerides with enzyme catalysis such as the processes described in U.S. Pat. Nos. 4,956,286, 5,697,986 and 5,713,965.
The main problem with background art processes for biodiesel production is that none of them completely addresses the production of biodiesel from low value high free fatty acid feedstocks. An economic analysis of any process for the production of biodiesel will indicate that feedstock cost is the largest portion of the production cost for biodiesel. A 15 percent free fatty acid (FFA) feedstock is the highest content that any contemporary commercial process proposes to handle; whereas, the actual feedstocks many producers will likely use (because of cost) will have up to 100 percent FFA content. Conventional acid catalyzed esterification of fatty acids is ill equipped to handle such a high FFA content.
Acid catalyzed esterification of fatty acids is not suitable for processing such high FFA concentrations. The amount of acid catalyst required to achieve high conversion rates in the esterification process increases with FFA concentration. This acid catalyst charge must be neutralized before processing the glycerides, and as the catalyst loading increases, the salt generated becomes excessive. These processes also generate a large volume of waste water as revealed by the disclosures of U.S. Pat. Nos. 4,303,590, 5,399,731 and 6,399,800. Alternatively, solid acid catalysts can be used for the fatty acid esterification reaction to avoid a neutralization step before the transesterification reaction. These processes have been extensively explored and documented, such as in U.S. Pat. No. 3,459,736 which uses titanium oxide as a catalyst, U.S. Pat. No. 4,698,186 which utilizes various solid acids as catalysts, U.S. Pat. No. 4,267,393 which uses sulfonated resins as solid acid catalysts and U.S. Pat. No. 5,908,946 which employs zinc and aluminum oxide as catalysts for the esterification reaction.
Enzymatic catalysis will readily esterify the free fatty acids, but this approach suffers reaction product inhibition from the presence of methyl esters when the fatty acids associated with mono-, di-, and tri-glycerides in the feedstock are to be esterified with enzymes. Another problem with enzymatic processing is the high cost of the catalyst. To avoid two-phase operation in packed bed and other reaction settings, some conventional processes for biodiesel production use high temperatures or volatile toxic co-solvents. Such a process has been investigated and claimed in U.S. Pat. No. 6,642,399 B2. Yet another problem with background art processes for producing biodiesel is that water is used to wash residual glycerin and salts from the FAMEs, generating a large volume of wastewater and potentially forming water and FAME emulsions as disclosed in U.S. Pat. No. 5,399,731.
Starrels in U.S. Pat. No. 1,659,790 discloses a method of producing commercial stearic acid. This invention is limited in that only an esterification step is disclosed.
Goss et al. in U.S. Pat. No. 2,290,609 discloses a process for producing fatty acid polyhydric esters. This invention is limited in that esterification must be followed by fractionation in a solvent system.
Dreger in U.S. Pat. No. 2,383,596 discloses a method for treating fatty acid glycerides. This invention is limited in that only an esterification step is disclosed.
Glossop in U.S. Pat. No. 2,383,599 discloses a method for treating fatty glycerides. This invention is limited in that free fatty acids must be separated from the fatty glycerides prior to alcoholysis.
Brokaw in U.S. Pat. No. 2,808,421 discloses a method for preparing mixed triglyceride compositions. This invention is limited in that a titanium alcoholate catalyst is required.
Birnbaum in U.S. Pat. No. 2,875,221 discloses a process for preparing monoglycerides of fatty acids. This invention is limited in that it requires admixing a substantial proportion of previously reacted monoglyceride product with a freshly mixed stream of glycerol and fat and rapidly heating the mixture on a hot surface.
Birnbaum in U.S. Pat. No. 3,102,129 discloses a process for producing monoglycerides of fatty acids. This invention is limited in that monoglycerides are produced, not methyl esters.
Erner in U.S. Pat. No. 4,364,743 discloses a synthetic liquid fuel and fuel mixtures. This invention is limited in that a process for the production and purification of alkyl esters of fatty acids is not disclosed.
Matsukura et al. in U.S. Pat. No. 4,371,470 disclose a method for manufacturing high quality fatty acid esters. This invention is limited in that a method for processing high free fatty acid feedstocks is not disclosed.
Billenstein et al. in U.S. Pat. No. 4,668,439 disclose a process for the preparation of fatty acid esters of short-chain alcohols. This invention is limited in that a process for use on high free fatty acid feedstocks is not disclosed.
Stern et al. in U.S. Pat. No. 4,695,411 disclose a process for manufacturing a fatty acid ester composition. This invention is limited in that an acid transesterification step must be followed by a basic transesterification step.
Holmberg et al. in U.S. Pat. No. 4,839,287 disclose a process for transesterification of triglycerides. This invention is limited in that the presence of a lipase enzyme is required.
Bam et al. in U.S. Pat. No. 5,424,467 disclose a method for purifying alcohol esters. This invention is limited in that the starting material must be a triglyceride. Moreover, while glycerin is recycled in the process, it is recycled downstream of the transesterification reactor.
Assmann et al. in U.S. Pat. No. 5,514,820 disclose a continuous process for the production of lower alkyl esters. This invention is limited in that the transesterification process must be carried out in at least two stages in a tube reactor. Moreover, the reference teaches that “it is particularly important to the transesterification reaction that no glycerol (reaction product) come into contact with starting oil” (col. 3, lines 4-7).
Wimmer in U.S. Pat. No. 5,434,279 discloses a process for preparing fatty acid esters of short-chain monohydric alcohols. This invention is limited in that glycerin produced by the transesterification process and previously separated off is added back to produced fatty acid ester.
Basu et al. in U.S. Pat. No. 5,525,126 disclose a process for the production of esters for use as a diesel fuel substitute. This invention is limited in that a catalyst comprising calcium acetate and barium acetate is required.
Stern et al. in U.S. Pat. No. 6,013,817 disclose a process for the production of ethyl esters. This invention is limited in that a process for the production of ethyl esters of fatty acids is disclosed. Moreover, this process uses water as an extractant for purification of the esters.
Jeromin et al. in U.S. Pat. No. 6,127,561 discloses a process for the production of monoglycerides. This invention is limited in that methyl esters are subjected to glycerolysis.
Peter et al. in U.S. Pat. No. 6,211,390 disclose a method for producing fatty acid esters. This invention is limited in that use of a near-critical extractant is required.
McDonald in U.S. Pat. No. 6,262,285 B1 discloses a process for dry synthesis and continuous separation of fatty acid methyl ester reaction product. This invention is limited in that the starting material must be a triglyceride. Moreover, the process is limited to mixing the alcohol and catalyst prior to feeding them to the transesterification operation.
Ergun et al. in U.S. Pat. No. 6,440,057 disclose a method for producing fatty acid methyl ester. This invention is limited in that crack emulsification of the contents of the transesterification reactor is required.
Thengumpillil et al. in U.S. Pat. No. 6,500,974 B2 disclose a process for preparation of a monoglyceride. This invention is limited in that the presence of a food grade polar solvent is required in the glycerolysis reactor.
Boocock in U.S. Patent Application No. 2003/0083514 A1 discloses a single-phase process for production of fatty acid methyl esters from mixtures of triglycerides and fatty acids. This invention is limited in that it requires acid catalyzed esterification of fatty acids prior to the transesterification step.
Fleisher in U.S. Patent Application No. 2003/0229238 A1 discloses a continuous transesterification process. This invention is limited in that use of a plug-flow reactor is required for the transesterification reaction.
The background art is also characterized by a number of non-patent publications. The limitations of the processes disclosed by these publications are described below.
Noureddini et al. in Glycerolysis of Fats and Methyl Esters, JAOCS, 1997, pp. 419-425, vol. 74, no. 4, AOCS Press, Lincoln, Nebr., discloses the glycerolysis of methyl esters and triglycerides with crude glycerin (glycerin). Glycerolysis of free fatty acids is not disclosed.
Tyson in Brown Grease Feedstocks for Biodiesel, WWW domain nrel.gov, 2002, pp. 1-33, National Renewable Energy Laboratory, Boulder, Colo., discloses techniques for converting greases to biodiesel. The techniques disclosed in this reference are limited in that washing of crude biodiesel with mildly acidic water is required. Moreover, the conditions taught for glycerolysis of free fatty acids (temperature in the range of 250° C. to 260° C. in the absence of a catalyst or 220° C. with a catalyst) would cause degradation of a major amount of the feedstock and loss of yield. The reference teaches that there is “no proven technology for 50+% FFA mixes” and that “combined processes for ASTM quality biodiesel not well developed, technical and economic questions exist.”
Tyson in Biodiesel Technology and Feedstocks, WWW domain nrel.gov, 2003, pp. 1-37, National Renewable Energy Laboratory, Boulder, Colo., includes much of the same information as contained in her 2002 presentation. The reference notes that using “glycerolysis to treat FFA” to “convert FFA to monoglycerides, then transesterify” is “commercial, not currently used in biodiesel.”
Davis Clements in Pretreatment of High Free Fatty Acid Feedstocks, Biodiesel Production Technology Workshop III, Mar. 26-28, 2003, pp. 78c-78i, Iowa State University, Lincoln, Nebr. discloses a number of methods for pretreatment of high free fatty acid feedstocks prior to transesterification. This invention is limited in that glycerolysis is carried out at 200° C. under an 11 pounds per square inch vacuum, usually with a catalyst such as zinc chloride, with venting of water. This invention is limited in that in the absence of a catalyst, a residence time of over 5 hours is required to achieve an effluent containing less than 1 percent free fatty acids.
In summary, the applicants are aware of no reports of using inexpensive feedstocks and effective technologies to produce fatty acid esters (biodiesel) economically and without environmental concerns. The current processes have the following drawbacks, which have been addressed in the process disclosed herein:
1. High temperatures and pressures,
2. Acid catalyzed esterification of fatty acids present in the starting material,
3. Use of toxic co-solvents,
4. Long processing times,
5. Low quality glycerin production, and
6. Using water to extract impurities from biodiesel.
In these respects, the conversion of high free fatty acid feedstocks to biodiesel according to the present invention substantially departs from the conventional concepts and designs of the background art, and in so doing provides a process and apparatus primarily developed for the purpose of producing fatty acid methyl esters and high quality glycerol from any low-value high free fatty acid feedstock.